fix: stabilize monitoring pagination and realtime counts

[seakee]

Summary

Fix monitoring account pagination and realtime row counts after v1.5.2.

Cause

Account summary pagination could be clamped back by stale remote page responses. Realtime rows also reused final stream totals, causing all rows in the same stream to show the same total call count.

Solution

• Add per-event realtime stream metrics in the usage service.
• Use per-event stream counts and recent patterns for realtime row display.
• Prevent stale account page responses from overriding the requested page.
• Add regression coverage for account pagination and realtime stream counts.

Testing

• go test ./...
• npm run type-check
• npm test

Fixes #154.
Fixes #155.